1. Field of the Invention
The present invention relates generally to a technique for reliably establishing a logical connection between desired nodes of a serial bus network such as IEEE-1394 or universal serial bus (USB) network.
2. Description of the Related Art
Serial Bus Protocol 2, known as SBP-2, is standardized by ANSI (American National Standards Institute) as ANSI-NCITS 325-1998 for allowing transfer of SCSI (Small Computer System Interface) data between nodes attached to an IEEE-1394 serial bus. The SBP-2 standard specifies an access protocol for establishing a logical connection between a node (called initiator) that asserts a collection request on the bus and a node (called target) that receives the request from the bus. Specifically, the access protocol specifies a login process for establishing a logical connection, a reconnection process for re-establishing the logical connection on the IEEE-1394 serial bus after the bus is reconfigured in response to a bus reset request, and a logout process for clearing the logical connection. A login process begins when an initiator makes a search through the network for a target node by examining the information stored in the configuration ROMs of all attached nodes. If such a target node is present, the initiator reads the address of the management agent register from the configuration ROM of the target node and writes the address of a login request in that register. In response, the target node sends a read request to the initiator, which replies with a login read response. The target node then requests the initiator to return its global unique identifier (i.e., node_vendor_id, chip_id_hi/chip_id_lo) by reading it from its configuration ROM. In response to the global unique identifier, the target node writes a login response into the login response register of the initiator and then reads the result of the login process (i.e., login status) from a status block and writes it into the status FIFO of the initiator. If the login process is successful, a logical connection has been established between the initiator and the target node.
Since a logical connection is established by a node when it wins the race in a login process, the SBP-2 access protocol is said to be based on a first-to-win principle. Assume that an IEEE-1394 serial bus network is comprised of two computers compliant with the SBP-2 standard and a hard disk drive which is specified as the target of one of the computers. If one of the computer succeeds in a login process, it obtains the right to use the hard disk drive as its peripheral device. However, the first-to-win scheme does not guarantee that the winner is always the desired computer of a peripheral device. Therefore, no SBP-2 compliant devices are currently available that can identify an initiator node for reliably establishing a logical connection to a target device.
It is therefore an object of the present invention to provide a connection controller and a method for a serial bus network for ensuring that an initiator node reliably establishes a logical connection to a target node.
According to a first aspect of the present invention, there is provided a connection controller for a serial bus network in which a plurality of layered protocols are provided to establish communication, the layered protocols including the protocol of a physical layer. The connection controller comprises physical layer processing circuitry for performing the protocol of the physical layer, and establishing communications with first, second and third nodes of the network, the first node being specified as an initiator node and the second node is a target node of the first node. Delay means is provided for introducing a delay time when the physical layer processing circuitry is energized. The physical layer processing circuitry is energized by power supplied from the first node for establishing a logical connection between the first and second nodes during the delay time and setting the third node in a disabled state during the delay time.
According to a second aspect, the present invention provides a connection controller for a serial bus network in which a plurality of layered protocols are provided to establish communication, the layered protocols including the protocols of a physical layer and a link layer The connection controller comprises first, second and third cable ports, the first cable port being connected to a first node. Physical layer processing circuitry, connected to the first, second and third cable ports and energized by power supplied from the first node through the first cable port, performs the protocol of the physical layer. Link layer processing circuitry performs the protocol of the link layer and is energized by power supplied from the first node through the first cable port. Control circuitry is connected to the physical layer processing circuitry via the link layer processing circuitry for determining whether second and third nodes are respectively present at the second and third cable ports, setting the third cable port in a disabled state immediately after the physical layer processing circuitry is energized while establishing a logical connection between the first and second nodes if the second and third nodes are determined to be present at the second and third cable ports, and setting the third cable port in an enabled state after the logical connection is established.
According to a third aspect, the present invention provides a serial bus network in which a plurality of layered protocols are provided to establish communication, the layered protocols including the protocol of a physical layer. The network comprises first, second and third nodes, and first, second and third cable ports, the first cable port being connected to a first node. Physical layer processing circuitry, connected to the first, second and third cable ports and energized by power supplied from the first node through the first cable port, performs the protocol of the physical layer. The first node determines a network topology of nodes connected to the second and third cable ports, determines from the network topology whether the second and third nodes are present at the second and third cable ports, respectively, disables the third cable port immediately after the physical layer processing circuitry is energized while establishing a logical connection with the second node, and enables the third cable port after the logical connection is established.
According to a fourth aspect, the present invention provides a method of controlling a serial bus network in which a plurality of layered protocols are defined to establish communication, the layered protocols including the protocol of a physical layer, wherein the network includes first, second and third nodes and physical layer processing circuitry associated with the first, second and third nodes for performing the protocol of the physical layer, wherein the first node is specified as an initiator node and the second node is a target node of the first node. According to the method, the physical layer processing circuitry is energized with power from the first node when the first node is powered on. In response to the application of power from the first node, the physical layer processing circuit establishes a logical connection between the first and second nodes while the physical layer processing circuitry is prevented from establishing a logical connection between the second and third nodes.
According to a further aspect, the present invention provides a processing circuit for a physical layer of layered protocols of a serial bus network, comprising a plurality of signaling ports, a port status control terminal, and an LSI chip connected to the signaling ports and the port status control terminal for performing the protocol of a physical layer, the LSI chip being responsive to a control signal received through the port status control terminal for holding a predetermined one of the signaling ports in a disabled state and holding the predetermined signaling port in an enabled state when the control signal changes state.
According to a still further aspect, the present invention provides a physical layer LSI chip for a physical layer of layered protocols of a serial bus network, comprising a plurality of signaling ports, timer means for measuring elapse of time from the instant the physical layer LSI chip is energized and producing a first signal when the measured time is smaller than a predetermined value and a second signal when the measured time is greater than the predetermined value, and port status control means for disabling a predetermined one of the signaling ports during the presence of the first signal of the timer means and enabling the predetermined signaling port during the presence of the second signal.